Stroke coded keyboard switch assembly

ABSTRACT

A stroke coded keyboard utilizes a switch matrix having crosspoints comprising deformable membrane switches. The crosspoints are connected in selected sequential pairs to deformable membrane contacts which define the elements or characters of the keyboard. An element can be keyed very rapidly by the stroke of a stylus on the top surface of the keyboard which sequentially closes the contacts defining the element. The keyboard can be utilized in many configurations such as a data entry keyboard, repertory dialer, or in parallel with or as a replacement for telephone keyboards. The character element is defined by the signals generated by a specified sequence of connections of i pairs of first (n) and second (m) conductors so that (nm) distinct characters can be defined on the keyboard by N + M conductors, where n and m are any positive integers greater than one and i is any positive integer greater than one or less than or equal to nm.

- United'States Patent [191- Hoffman i5 1 STROKE comm KEYBOARD swrrcn [73] Assignee: Bell Telephone Laboratories,

7 Incorporated, Murray Hill, NJ.

[22] Filed: Aug. 30, 1971 [21] Appl. No.: 175,879

[52] US. Cl. 200/1 R, 200/5 R, 200/159 B [51] Int. Cl. H01h 41/00 [58] Field of Search 200/5, 159 B;

[56] 1 References Cited UNITED STATES PATENTS 3,676,615 7/1972 Wiedmer .l 200/5 R X 3,308,253 3/1967 Krakinowski... 200/159 B UX 3,472,974 10/1969 McGough 179/90 K 3,600,528 8/1971 Leposavic 200/5 A 3,544,987 12/1970 McMann, Jr. et al. 200/5 R X 3,591,749 7/1971 Comstock 200/159 B X 3,290,439 12/1966 Willcox et a1... '200/5 A X 3,584,162 6/1971 Krakinowski 200/5 A Primary Examiner-J. R. Scott Anomey-W. L. Keefauver et al.

111 3,743,797 [451 July 3,1973

[5 7] ABSTRACT A stroke coded keyboard utilizes a switch matrix having crosspoints comprising deformable membrane contacts or switches. Each keyboard character or element is defined by the signals generated by the closure of contacts which produce a specified sequence of connections of 1' pairs of first (n) and second (m) conductors so that (nm)" distinct characters can be defined on the keyboard by n+n1 unique conductors, where n and m are any positive integers greater than one and i is any positive integer greater than one and less than or equal to nm. An element can be keyed very rapidly by the stroke of a stylus on the top surface of the keyboard which sequentially closes the contacts definingthe element. The keyboard can be utilized in many configurations such as a data entry keyboard, repertory dialer, or in parallel with or as a replacement for telephone keyboards.

The character element is defined by the signals generated by a specified sequence of connections of i pairs of first (n) and second (m) conductors so that (nm') distinct characters can be defined on the keyboard by N M conductors, where n and m are any positive integers greater than one and i is any positive integer greater than one or lessthan or equal to nm.

16 Claims, 5 Drawing Figures Patented July 3, 1973 5 Sheets-Sheet 1 FIG.

FIG. 2

Patented July 3, 1973 3,743,797

5 Sheets-Sheet 2 FIG. 3

FIG. 4

[SAVfCTLG/SH/FfSPK/ 96/ O /VUMBEOMBK$P I Patented July 3, 1973 3,743,797

5 Shoots-Sheet :5

FIG. 5

GANGL/NGER M. FR/CKERT MEI/4! KLEBST 72 C FREEMB/SH (as (92 96W [98 [m0 STROKE MATRlX FEQ E E AHE I JEY c o o e o DECODER SIGNAL COUPLER TELEPHONE GENERATOR 94 TIMING AND CONTROL Patented July 3, 1973 3,743,797

5 Shoots-Sheet 5 9 EQ IIIIIHI DEEIEGCAIIIATAICN D%:SI%%AQ)LN OFCROSSPONTS vI v2 v3 v4 HI H2 H3 H4 B4 8352 8| 0 I I o o 0 o I I o 0 0 2 I I o o I o 3 I l o 0 I I 4 I I O I O O 5 I o I o 6 I I o I I o 7 I I o I I I a I I I 0 o o 9 I I I o 0 I I0 I I I 0 0 II I I I 0 I I I2 I I I o 0 I3 I I l I o I I4 I I I l 0 I5 I I I I FIG. [0

HI FI I 2 3 H2 '4 5 s 7' H3 8 9 I0 IILL H4 12 Iiffi 80 VI v2 v3 v4 82 f i i MATRIX I LOW Q E) BIT 05 GROUP HAIGTH 02 03 04 GROUP 84 WHIHHHH A8 A7 5 4 3 A2 AI G' I P b7 b6 b5 b4 b3 b2 bl r86 8 BIT BUFFER REGISTER STROKE CODED KEYBOARD SWITCH ASSEMBLY BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to keyboards and more particularly to miniature stroke coded keyboards for use in a telephone system in such applications as telephone keyboards, data entry keyboards and repertory dialers.

2. Description of the Prior Art The telephone network is finding increasing usage for the transmission of data such as computer input and output data, inventory control data, sales or order data, etc. Presently, most data of the previously mentioned types is transmitted through the use of teletypewriter sets or through multi-frequency signaling means of a multi-frequency signaling push-button telephone. Teletypewriter sets are not always readily available where needed and, additionally, are too expensive to be economically feasible for the part-time user. Multiple-key encoding of information by means of a push-button telephone set is relatively slow and may be inconvenient in a desk-top environment where encoding concurrently with pencil calculations or writings is desirable. Thus a need remains for a keyboard or interface which has greater efficiency than multiple-key encoding and is sufficiently flexible to permit efficient usage in different environments while simultaneously being economically feasible.

Accordingly, it is an object of this invention to enhance the efficiency of keyboards for accessing the telephone network.

Another object is to improve the flexibility of keyboards to make their use more convenient in various environments.

Another object is to improve keyboards to provide more rapid encoding of information than is possible with multiple-key encoding.

SUMMARY OF THE INVENTION The foregoing objects and others are achieved in accordance with the principles of this invention through the use of a miniature stroke coded keyboard which can be used as a replacement for, or in parallel with, a multifrequency signaling push-button telephone keyboard. The keyboard has an (n X m) crosspoint matrix of pressure sensitive diaphram switches which define (n X m) unique crosspoints but which require only (n m) output leads. The unique crosspoints are elecrically I connected in prescribed combinations to contacts which define specific keyboard characters or elements such as letters, numbers, computer instructions and the like which are indicated by the keyboard keys. Different orders of coding can be provided by defining the keyboard elements by different numbers of crosspoints. The keyboard elements or characters are keyed by stroking the pressure sensitive diaphram with a stylus thereby sequentially closing the normally open contacts. The keying of information can be accomplished much more quickly than by multiple-key encoding because of the stroking action. A single keyboard can be used for all encoding or, alternatively, special purpose keyboards can be designed for specific applications thereby giving an optimum layout of keyboard elements.

BRIEF DESCRIPTION OF THE DRAWING The invention will be more fully comprehended from the following detailed description and accompanying drawing in which:

FIG. 1 is an exploded perspective view of a stroke coded keyboard in accordance with the invention;

FIG. 2 is a schematic representation of the keyboard of FIG. 1;

FIG. 3 is an enlarged schematic representation of portion 333 of FIG. 2;

FIG. 4 is an exploded perspective view of a special purpose keyboard and a holder for mounting the keyboard;

FIG. 5 is a perspective view of another special purpose keyboard which can be used with the holder of FIG. 4;

FIG. 6 is a block diagram representation of a stroke coded keyboard system including auxiliary apparatus for improving keyboard operation;

FIG. 7 is a timing diagram for the system of FIG. 6;

FIG. 8 is a schematic representation of a keyboard for generating the USASCII code;

FIG. 9 is a truth table for the keyboard of FIG. 8; and

FIG. 10 is a schematic representation of a system for implementing equations derived from the truth table in FIG. 9.

DETAILED DESCRIPTION FIG. 1 is an exploded perspective view of a stroke coded keyboard 101 in accordance with the principles of the invention. Keyboard 101 comprises a sandwich construction including a base assembly 2, an overlaying insulating spacer 4, and a deformable or flexible membrane 6 overlaying spacer 4. Assembly 2, spacer 4 and membrane 6 can be adhered or joined together by an appropriate adhesive such as commercially available pressure sensitive adhesive. Base assembly 2 can comprise a substrate 8 of glass, ceramic, or other suitable material having a pattern of conductors 10 and lands 11 on the top surface thereof. Conductors 10 and lands 11 can be formed by well known techniques such as vacuum deposition of gold and photo-etching.

Spacer 4 comprises a thin sheet 12 of insulating material having a number of openings 14 therein for reasons to be subsequently explained. A suitable spacer 4 can be formed by mechanically making openings in a thin sheet of material such as a polyester film which is commercially available. Spacer 4 can also be formed from a photosensitive material by known masking and etching techniques.

Deformable membrane 6 comprises a thin sheet 16 of flexible insulating material, such as the previously mentioned polyester film or acetate, having a pattern of conductors l8 and lands 19 on the bottom surface thereof. Conductors l8 and lands 19 can be formed by the previously mentioned vacuum deposition of gold or by other techniques known in the art. The keyboard keys indicating the characters or elements of the keyboard are designated on sheet 16. Sheet 16 has a smooth top surface 20 which is wear resistant to strokes of a stylus for reasons to become apparent subsequently. When pressure is applied to-top surface 20 by means of a stylus or pencil, sheet 16 deforms through any opening 14 under the stylus so that any land 19 aligned with opening 14 will contact any land 11 on substrate 8 which is also aligned with the opening 14.

Thus lands 11 and 19 can be utilized as respective terminals of a contact or switch as will be subsequently shown. The pressure required for deforming sheet 16 to cause contact between lands 11 and 19 depends upon such factors as the thickness and resulting flexibility of sheet 16, the thickness of spacer sheet 12 and the size of openings 14. A pressure range from a few grams to several ounces is easily obtainable. Openings 14 are usually large with respect to the thickness of sheet 12 and thus the relative dimensions shown are for illustration only.

The intersection of conductors 22 and 24 on substrate 8 and sheet 16, respectively, at which points lands 23 and 25 are located, define the crosspoints of a switch matrix which is the foundation for the keyboard of this invention. The crosspoints can be closed and thereby a connection completed by deforming membrane 6 as previously discussed. A (4 X 4) matrix having 16 crosspoints is shown and described in detail below. However, it will be readily apparent that the following discussion would apply equally as well to a (n X m) matrix where n and m may be any desired positive integers.

Referring now to FIG. 2 and 3, the construction of the keyboard of FIG. 1 is schematically illustrated. Four horizontal conductors 30, 32, 34 and 36 and four vertical conductors 38, 40, 42 and 44 of a matrix 31 define 16 unique crosspoints or contact points P1, P2, P16 while requiring only 8 output leads which may be readily combined into a single multiconductor cable 46. Matrix 31 could itself be used as a simple keyboard having 16 elements or characters each of which is defined by one of the crosspoints P1 P16 comprising diaphragm or membrane switches. The term element or character is used herein generically to include numbers, letters, mathematical functions such as plus and minus and computer instructions, etc., which comprise the keys of various types of keyboards. These switches could be activated and thereby the keyboard elements keyed by deforming the flexible diaphragm as previously discussed. However, in most applications a keyboard having only sixteen distinct elements would not be adequate. According to applicant's invention, the keyboard elements are defined by sequential combinations of more than one crosspoint so that a large number of distinct keyboard elements can be obtained without losing the advantages of using a small matrix, i.e., limited number of output leads, extremely small keyboard size, etc. In essence, defining each keyboard element by a single crosspoint can be considered as firstorder coding. Defining an element by two crosspoints constitutes second-order coding, etc. The number of unique keyboard elements which can be defined by a matrix is x where x is the number of matrix crosspoints and i is the order of the coding.

In applicants illustrative embodiment, second-order coding is utilized, i.e., each keyboard element is defined by a'sequential pair of crosspoints. Hence the 16 crosspoints of the (4 X 4) matrix can define 256 distinct keyboard elements, i.e., 16. The specification of a sequential pair of crosspoints determines both the crosspoints to be utilized in defining the element and the manner in which the crosspoints are connected to the element as will be shown subsequently.

The term defining a keyboard element" means that the matrix crosspoints chosen to define the element are electrically connected to respective contact terminals under the face of the element which can then be operated by keying the element, i.e., applying pressure to the keyboard key indicating the element as previously discussed. For example, the sequential pair of crosspoints P1 andP2 can be specified as defining keyboard element N which may be a number, letter, computer instruction, etc. Crosspoints P1 and P2 are connected to element N in a manner such that when element N is keyedin the proper way, the output from key- 1 of vertical conductor 38 and horizontal conductor 30.

P1 is operated, thereby connecting conductors 30 and 38, by applying pressure to the keyboard where crosspoint P1 is located. This can be represented by the closure of a switch 31. Crosspoint P2 is defined by the intersection of vertical conductor 40 and horizontal conductor 30 and the operation thereof can be represented by the closure of switch 33. In defining element N by the sequential pair of crosspoints P1 and P2, the conductors defining P1 and P2 are connected to terminals of respective contacts or switches located under the face of element N. That is, conductors 38 and 30, defining crosspoint P1, are connected to respective terminals of contact or switch 35. Conductors 40 and 30, defining crosspoint P2, are connected to respective terminals of contact 37. In essence, contacts 35 and 37 are in parallel with crosspoints P1 and P2, respectively, and the closure of contact 35 or 37 appears the same as the closure or operation of P1 or P2, respectively, with respect to the signal on cable 46. Because element N is defined by the sequential pair of crosspoints P1 and P2, the output on cable 46 is interpreted as element N whenever crosspoints P1 and P2 are operated in the indicated sequence, or alternatively whenever contacts 35 and 37 are closed in that order. p

In the illustrative embodiment, the horizontal conductor 30 is connected to contact terminals which comprise lands 19 on membrane sheet 16. Vertical conductors 38 and 40 are connected to respective contact terminals which comprise lands 11 on substrate 8. Thus contacts 35 and 37 are sequentially closed by sequentially applying pressure to the surface of mem-- brane 6 where the appropriate lands are located, i.e., applying pressure to the keyboard key indicating element N. Because contacts 35 and 37 are in parallel with crosspoints P1 and P2, respectively, and the operation of the contacts produces the same output as the operation of the respective parallel crosspoint, it is not necessary that matrix 31 itself physically appear on the keyboard. That is, the contacts themselves act essentially as matrix crosspoints which are located in a pattern other than a standard matrix pattern.

Pairs of mating lands 11 and 19 representing the terminals of respective contacts 35 and 37 are aligned with closely adjacent openings 14 in spacer 12 and the pair of contacts is labeled as the single key N representing element N on the surface of membrane sheet 16. Element N can then be keyed by applying pressure to sequentially deform membrane 6 through the respective openings 14 thereby sequentially closing contacts 35 and 37. The keying advantageously can be done very rapidly by stroking a stylus, pencil or the like across the face of key N, i.e., from top to bottom in the illustrative embodiment. The stroke keying or coding technique offers significant advantages, especially in speed and ease of keying, over techniques such as multiple depressions of buttons or keys required by other keyboards. The stroke keying or coding is permitted by the smooth upper surface of membrane sheet 16.

The crosspoints P1 and P2 can be used to define a second keyboard element M when designated as the sequential pair P2 and P1. This is possible because the sequence of closures for the pair P2 and P1 is different from the sequence of closures for the pair P1 and P2 used to define element N. If element M is defined by the sequential contact pair P2 and P1 then the connections 48 and 50 are connected to the bottom and top portions, respectively, of keyboard element M. Thus element M is keyed or coded by a stylus stroke from top to bottom on the face of the key representing element or character M. All other elements on the keyboard are defined similarly by connection from specified combinations of the matrix crosspoints to respective top and bottom portions of the elements.

Ordinarily it is desirable for all keyboard elements to be coded by stylus strokes in the same direction, i.e., from top to bottom on the element face in the illustrative embodiment. However, if strokes in other directions are permitted, various keyboard elements can be combined into a single composite key, the output from which will be dependent upon the stroking direction. For example, illustrative elements N and M could be combined into a single keyboard key, the output from which represents element N when the composite key is stroked from top to bottom and which represents element M when the composite key is stroked from bottom to top. Such composite keyboard keys might be desirable on an alphanumeric keyboard where both upper and lower case characters are needed but where keyboard space is limited. In such case for example, a top to bottom stroke could key a capital letter while a bottom to top stroke on the same keyboard key could key the corresponding lower case letter.

As previously mentioned, the keyboard of this invention can be used as a substitute for, or in parallel with, a regular multi-frequency signaling push-button telephone keyboard. Different versions of the keyboard can be designed as alphanumeric terminals, calculator terminals, repertory dialers, special business terminals such as for placing merchandise orders, and numerous other special applications. Because all coding is done on the keyboard itself through the specification of the specific pairs of crosspoints which define the keyboard elements, the output leads from the keyboard, i.e., the leads from the crosspoint matrix, remain fixed regardless of the specific type keyboard being used. Thus a basic keyboard structure with interchangeable keyboards can be utilized.

FIG. 4 shows a basic keyboard holder 52 and one version of a keyboard 54 which can be used therewith. Holder 52 includes a frame 56 which defines a compartment 58 into which keyboard 54 can be slid. A lip or flange 60 around the periphery of frame 56 holds keyboard 54 in position. Holder 52 also includes eight contacts 62 which connect with the eight output leads from the 4 X 4 crosspoint matrix which is utilized. These output leads normally terminate in printed circuit lands on the bottom surface 55 of keyboard 54. The contacts 62 terminate multiconductor cable 64 which connects the keyboard assembly into the telephone system.

Keyboard 54 is constructed as previously described with reference to FIG. 1 through FIG. 3. The eight output leads from the matrix can be in the form of printed circuit conductors and contact terminals on the bottom side 55 of the keyboard. Because all conductors and contacts are formed by printed circuit techniques and a stylus is used for keying, the keyboard can be made quite small in size. Keyboard 54 advantageously can be the approximate size of a standard credit card so that it can be conveniently carried for use wherever needed. In the illustrative embodiment keyboard 54 is designed for use as a calculator terminal in conjunction with a computer such as a time-shared computer or the like". A total of 48 keyboard elements is illustrated including numbers, computer instructions and local controls such as ON and OFF for controlling the keyboard operation. The numbers and types of keyboard elements indicated is purely illustrative. Any number of elements up to 256 could be utilized. The elements of keyboard 54 are defined as previously discussed with respect to FIG. 1 through 3.

Normally it is necessary to dial or key a telephone number to access a computer from a remote terminal. This is especially true in commercial time-shared computer systems. Keyboard 54 is designed to permit this dialing by underlining the keyboard title, i.e., drawing a line through the series of contacts represented by dots 66 under the title CALCULATOR. Each dot 66 is a contact connected to a matrix crosspoint representing a digit of the desired telephone number. Thus dots 66 define element 67 in the same manner as other keyboard elements except that more crosspoints are utilized in the definition. For example, the contacts represented by dots 66 define keyboard key or element 67 in the same manner as contacts 35 and 37 define keyboard element N in FIGS. 2 and 3. The designation of the particular terminal or user also can be keyed by underlining such designation on the keyboard, i.e., keying element 69 by stroking through dots 68 which comprise digits or numbers in the designation. Each of the other keyboard elements or keys such as ACl, AC4, COS, CALL, etc., are defined by a unique combination of crosspoints in the same manner as previously discussed with reference to FIGS. 2 and 3.

A second type of keyboard 70 for use in frame 56 is shown in FIG. 5. Keyboard 70 essentially serves as an inexpensive telephone repertory dialer. The keyboard elements 71 representing the telephone numbers comprise contacts represented by the dots 72 under the names listed. Each contact or dot is connected to a crosspoint representing a digit. The telephone numbers are keyed or dialed by a simple stroke of the stylus through the dots 72 underlying the desired name. Different keyboards 70 representing different repertory dialers can for example be made for business numbers, personal numbers, etc., and used interchangeably in holder 56.

It should be apparent from the foregoing examples and discussion that numerous types of keyboards for special applications can readily be designed. The basic apparatus, i.e., the number of output leads, the keyboard holder, etc., can remain fixed in all such keyboards. The coding for special applications is designed into the keyboard elements and thus the layout, appearance, etc., of any keyboard can be optimized for its specific application. The keying by stylus strokes can be utilized on all such keyboards for efficient keying operation. I

The keyboards of this invention can be utilized as replacements for, or in parallel with, a standard multifrequency signaling push-button telephone keyboard. When used in the former application the keyboard can utilize the basic circuitry of the telephone set including the multi-frequency signal generator therein to produce its output signals. In the latter application the keyboard can also utilize the basic telephone set circuitry. In such case an appropriate connection such as a pin and socket connector can be provided on the telephone set for connecting the keyboard into the telephone set circuitry at the appropriate points. Alternatively, the keyboard can have its own self-contained auxiliary circuitry such as a multi-frequency signal generator.

FIG. 6 is a block diagram of a keyboard system in which a stroke coded keyboard 88 is utilized in conjunction with additional apparatus for enhancing the operation of the stroke coded keyboard. When the elements of keyboard 88 are stroked very rapidly, the pulse duration upon contact closure may not be sufficient for compatability with the telephone switching network. Further, the spacing required between pulses by the switching network may be greater than that obtained during rapid keying strokes. Accordingly, timing and control unit 94 can contain well known circuitry such as monostable multivibrators for insuring proper pulse duration and separation.

Another problem which may be encounted in using stroke coded keyboard 88 is contact bounce which causes uncertainty whether or not an element has actually been keyed. A simple resistive-capacitive integration circuit in timing and control unit 94 can minimize this problem by integrating the contact closure signals for a short period. The multivibrators previously mentioned also help eliminate the problem of contact bounce.

Circuitry advantageously can be provided in timing and control unit 94 for grouping the contact closure signals from keyboard 88 into the correct pairs representing a specific keyboard element. For example, if the keyboard elements are defined by pairs of contacts the grouping circuitry can provide for the cancellation of a contact closure signal after a specified interval if the second contact closure signal of the pair has not been received. This grouping feature can be of significant value in reducing errors in coding. The grouping circuitry will require a small memory in timing and control unit 94 for efficient operation. The functioning of grouping circuitry will be explained with reference to FIG. 7 showing a timing diagram therefor.

The timing periods for the grouping circuit can be established by well known techniques such as by monostable multivibrators. At point 108 in the timing diagram the first contact used in defining a keyboard element is closed by pressure from a stylus. The signal representing this closure is stored in the previously mentioned memory and a feedback such as an audible click or blinking light can readily be provided to indicate keying of this first contact. At point 102 the contact is released when the operating pressure is removed and also a multivibrator fires to initiate timing period T3. At point 104 the second contact used in defining the keyboard element is closed by stylus pressure. If the time period T1 between the release of the first contact at point 102 and the closure of the second contact at point 104 is less than the timing period T3, the second contact closure is grouped with the first closure to register the completion of the keying of the indicated keyboard element and the appropriate signal is then transmitted to the telephone network. If period Tl exceeds time period T3, i.e., a second contact closure has not been made in the time period T3, the first contact closure is erased from the memory at point 105 at the end of period T3 and the next contact closure is treated as the first contact closure in the keying of another keyboard element. 7

When the second contact closure is made at point 104, a second multivibrator is also fired initiating timing period T4 which ends at point 107. Period T2 indicates the length of time that the second contact remains closed. If period T2 exceeds timing period T4, the grouping circuitry will continue repeating the keyboard element which has just been keyed with the proper signal duration, etc., until the pressure is removed and the contact is opened. A multivibrator is fired at the termination of period T2 at point 106 to initiate timing period T5. Timing period T5 is the period of time required to elapse after the completion of keying one keyboard element at point 106 until the keying of a subsequent keyboard element can be initiated at point 109. If the actual period T6 between points 106 and 109 is less than timing period T5 the contact closure at point 109 is not recognized and the multivibrator is refired to reinitiate timing period T5.

Timing periods T3 and T5 are specified to give minimal error rates from such factors as overstroking an element or inadvertent stroking or poking an element. The optimum timing periods may vary depending on the type of keyboard being utilized, the training of the operator, etc. Timing period T4 is selected to give acceptable repeat operation of keyboard elements.

The output from the stroke coded keyboard 88 on the eight output leads previously mentioned is fed to matrix decoder 92 which decodes this output to determine the crosspoints which define the keyboard element which has been keyed. Decoder 92 comprises well known logic circuitry for producing an output signal responsive to the particular input terminals on which an input signal appears. Decoder 92 can also include buffer-amplifiers for providing the proper levels to the output of decoder 92. The output from decoder 92 controls multi-frequency signal generator 96 which produces the actual tones by which information is transmitted from keyboard 88 to the telephone network. Generator 96 can be the same unit as that used to generate the signaling tones in a standard multifrequency signaling telephone. Alternatively, generator 96 can be an integrated circuit tone generator in order to have a size more compatible with the minature size of keyboard 88.

When used in parallel with a telephone keyboard, keyboard 88 must be coupled to the telephone by an appropriate coupler 98. Coupler 98 can comprise an acoustic coupler known in the art which fits over the telephone set mouthpiece and acoustically couples signals from generator 96 into telephone set 100. Coupler 98 can also comprise circuitry as previously mentioned which electrically couples the signals from generator 96 into telephone set 100 at the appropriate points.

The principles of this invention can be used in a keyboard which, along with some simple logic circuitry, can be utilized to generate special codes such as the United States American Society for Communication and Information Interchange Code (USASCII Code). Because the USASCII Code contains 128 elements, a (4 X 4) matrix using second-order stroke coding is sufficent to generate the complete code because as previously mentioned such a matrix can define up to 256 unique characters.

The USASCII Code is an eight bit code comprising seven information bits and a parity bit for each character. The parity bit can be grouped with the information bits and these eight bits then can be broken into two bit groups, designated the high bit group and low bit group, each having four bits. Each bit group can be represented by an equivalent decimal number between zero and 15. As schematically illustrated in FIG. 8, the crosspoints 74 of the (4 X 4) switch matrix can also be designated between zero and and the appropriate combination of crosspoints can be connected to the designated character defined thereby on keyboard 78.

From the truth table shown in FIG. 9, logical equations sufficient to define each bit position B for each bit group can be derived as follows:

i L for the low bit group;

i= H for the high bit group;

B the least significant digit in the bit group, etc.;

V V V., the second, third and fourth columns or vertical conductors in the matrix, respectively; and

H H H, the second, third and fourth rows or horizontal conductors in the matrix, respectively. Thus, for example, USASCII element Al on keyboard 78 might be defined by the decimal designation 04,06 which is represented by the connections 77 and 79 from crosspoints 4 and 6, respectively, to the top and bottom contacts respectively, defining element Al. The sequential closure of the top and bottom contacts under element A1 will produce the USASCII character 010001 10 which is the binary representation of 04,06. This designation or definition of element Al represents the character F with odd parity in the actual USAS- CII Code. A USASCII binary character can in general be represented by P b b b b b b b, where:

2 21. a ar. 4 84L where:

b the least significant bit in the character, etc.; and

P the parity bit.

The logical equations representing the bits can be implemented and thereby the USASCII characters generated by the simple two-level logic illustrated in FIG. 10. The outputs of the USASCII stroke coded keyboard 80 are fed to a matrix decoder 82 such as that previously discussed. The outputs from matrix decoder 82 are combined by OR gates 02, 03, 04, and 05. The outputs are also connected to OR gate 01 which triggers timing and control unit 84. Timing and control unit 84 includes substantially the same apparatus as that previously discussed with respect to timing and control unit 94 in FIG. 6. Unit 84 also gates the outputs from OR gates 02 through 05 into appropriate bit positions in buffer register 86 by triggering AND gates Al through A8. The data stored in register 86 is in the USASCII format comprising seven information bits b through b and one parity bit P and can be outputed either serially or in parallel. Timing and control unit 84 resets buffer 86 as needed after inputs are taken therefrom. Register 86, OR gates 01 through 05 and AND gates Al through A8 comprise circuits well known in the art.

While the invention has been described with reference to specific embodiments thereof, it is to be understood that various modifications thereto might be made by those skilled in the art without departing from the spirit and scope of the following claims.

What is claimed is:

1. A keyboard having a plurality of keys indicative of a plurality of characters comprising a substrate having first conductors thereon, an insulating spacer positioned on said substrate and having openings therethrough, and a deformable membrane positioned on said spacer and adapted for movement through said openings, said membrane having second conductors thereon, characterized in that:

each of said characters is defined by signals generated by connections of a plurality of said first conductors with a plurality of said second conductors in a specified sequence; and

said keyboard includes means responsive to a pressure stroke in a first direction applied across one of said keys for establishing said connections in a first one of said specified sequences and for generating said signals indicative of a first one of said characters.

2. Apparatus in accordance with claim 1 wherein said first conductors comprise n unique conductors, said second conductors comprise m unique conductors, and said character is defined by said signals generated by said specified sequence of connections of 2' pairs of said first and second conductors so that (nm) distinct characters can be defined on said keyboard by n+m unique conductors, where n and m are any positive integers greater than one and i is any positive integer greater than one and less than or equal to nm:

3. Apparatus in accordance with claim 2 where n and m each equal four and i equals two whereby 256 distinct characters can be defined on said keyboard by eight unique conductors.

4. Apparatus in accordance with claim 1 wherein said responsive means comprises:

a plurality of first contact members within designated switching areas on said substrate, said first contact members withineach of said switching areas being connected to a respective one of said plurality of first conductors; and

a plurality of second contact members within areas defined by said keys on said membrane corresponding to said switching areas, said second contact members within each of said defined areas being connected to a respective one of said plurality of second conductors, said first and second contact members being arranged for sequential connection of respective ones thereof in response to said pressure stroke.

5. Apparatus in accordance with claim 1 wherein said one of said keys is indicative of a plurality of said characters and said responsive means is responsive to a pressure stroke applied across said one of said keys in a second direction for establishing said connections in a second one of said specified sequences and for generating said signals indicative of a second one of said characters.

6. Appparatus for generating encoded electrical signals comprising, in combination:

a keyboard structure having a plurality of keys indicative of a plurality of characters;

first and second groups of conductors, a plurality of said first and second groups of conductors being associated with one of said keys; and

means responsive to a pressure stroke applied across said one of said keys in a first direction for connecting said plurality of said first group of conductors to said plurality of said second group of conductors in a first sequential order and for generating signals indicative of a first one of said characters.

7. Apparatus in accordance with claim 6 including means for grouping said signals into said first sequential order representing the keying of said first one of said characters so that errors in said keying can be reduced, comprising:

first means for designating the first of said signals asthe first signal in said first sequential order; first timing means for initiating a first timing period upon the completion of said first signal;

second means for designating the second of said signals as the second signal in said first sequential order when said second of said signals is received before the expiration of said first timing period, said second designating means being responsive to said first timing means to reject said second of said signals and to initialize said first designating means by removing said first signal therefrom when said first timing period expires before said second of said signals is received so that signals caused by inadvertent touching of said keys can be eliminated.

8. Apparatus in accordance with claim 7 wherein said first timing period has a duration adapted to cause rejection of signals produced by discrete pokes on said keys and to cause signals produced by strokes on said keys to be designated as signals in said first sequential order.

9. Apparatus in accordance with claim 7 including a second timing means for initiating a second timing period when said second of said signals is received before the expiration of said first timing period; and

third means for repeatedly designating said first and second ofsaid signals as said first and second signals, respectively, in respective ones of said first sequential orders when said second of said signals has a duration greater than said second timing period, said third designating means being responsive to the termination of said second of said signals to cease operation whereby automatic repeat keying of said first one of said characters can be obtained.

10. Apparatus in accordance with claim 7 including a third timing means responsive to the termination of said second of said signals for initiating a third timing period; and

means for rejecting subsequent ones of said signals until the expiration of said third timing period thereby to eliminate signals caused by keying strokes extending beyond said one of said keys.

11. Apparatus in accordance with claim 10 including means for reinitiating said third timing period when any signal subsequent to said second of said signals is received before the expiration of said third timing period.

12. Apparatus in accordance with claim 6 wherein said one of said keys is indicative of a plurality of said characters and said responsive means is responsive to a pressure stroke applied across said one of said keys in a second direction for connecting said plurality of said first group of conductors to said plurality of said second group of conductors in a second sequential order and for generating signals indicative of a second oneof said characters.

13. Apparatus in accordance with claim 6 wherein said responsive means comprises a group of switches, a plurality of said switches being operably associated with one of said keys, a pair of said conductors from said first and second groups being associated with each of said switches for establishing a connection therebetween, said switches being arranged for operation in a first sequence in response to said pressure stroke in said first direction for connecting said conductors in said first sequential order.

14. Apparatus in accordance with claim 13 including:

means for suppressing spurious signals caused by contact bounce when said switches are operated, said suppressing means including an integration circuit; and

means for controlling the duration and spacing of sig-.

nals generated when said switches are operated. 15. A keyboard each character of which is keyed by a pressure stroke in a specified direction within an area designated by said character on the surface of said keyboard to produce a preselected sequence of signals in an output circuit representing said character, comprising, in combination:

a substrate having thereon a plurality of first contact members located in switching areas corresponding to said designated areas, and a plurality of first conductors each of which is connected to preselected ones of said first contact members;

an insulating spacer mounted on said substrate and having apertures therein aligned with said first contact members;

resilient membrane mounted on said spacer and forming said surface of said keyboard and having said characters designated thereon, said membrane having on a major surface thereof a plurality of second contact members within said designated areas, said second contact members within a designated area being aligned with corresponding ones of said first contact members in a respective one of said switching areas through said apertures, and a plurality of second conductors each of which is connected to preselected ones of said second contact members, one of said signals being produced when one of said first conductors is connected to one of said second conductors, said membrane being adapted'for movement through said apertures in response to said pressure stroke to connect said plurality of second contact members within said designated area with said corresponding ones of said first contact members within said respective switching area for connecting respective ones of said first conductors to respective ones of said second conductors, said first and second contact members being arranged for sequential connection to produce said preselected sequence of signals.

16. A keyboard each character of which is keyed by a pressure stroke within an area defined by said charac ter on the surface of said keyboard, said character being represented by signals generated by the connection of two first conductors with two second conductors in a specified sequence by said pressure stroke, comprising, in combination:

a substrate having thereon a plurality of said first conductors and a plurality of first contact members, first and second ones of said first contact members being respectively located within first and second portions of respective switching areas designated on said substrate, first and second ones of said first conductors being respectively connected to said first and second ones of said first contact members within said first and second portions of said switching area;

a spacer on said substrate having openings therethrough aligned with respective ones of said first contact members; and

a deformable membrane comprising said surface of said keyboard and having said defined areas thereon, said membrane having thereon a plurality of second contact members and a plurality of said second conductors, first and second ones of said second contact members being respectively located within first and second portions of said defined area, said first and second ones of said second contact members in said first and second portions of said defined area being respectively aligned through said openings with said first and second ones of said first contact members in said first and second portions of a corresponding one of said switching areas, first and second ones of said second conductors being respectively connected to said first and second ones of said second contact members within said first and second portions of said defined area, said membrane being adapted for movement through said openings in response to said pressure stroke to effect contact between said first and second ones of said second contact members within said defined area and said respective first and second ones of said first contact members within said corresponding switching area in a sequential order thereby connecting said first and second ones of said first conductors, respectively, to said first and second ones of said second conductors in said specified sequence to represent said character. 

1. A keyboard having a plurality of keys indicative of a plurality of characters comprising a substrate having first conductors thereon, an insulating spacer positioned on said substrate and having openings therethrough, and a deformable membrane positioned on said spacer and adapted for movement through said openings, said membrane having second conductors thereon, characterized in that: each of said characters is defined by signals generated by connections of a plurality of said first conductors with a plurality of said second conductors in a specified sequence; and said keyboard includes means responsive to a pressure stroke in a first direction applied across one of said keys for establishing said connections in a first one of said specified sequences and for generating said signals indicative of a first one of said characters.
 2. Apparatus in accordance with claim 1 wherein said first conductors comprise n unique conductors, said second conductors comprise m unique conductors, and said character is defined by said signals generated by said specified sequence of connections of i pairs of said first and second conductors so that (nm)i distinct characters can be defined on said keyboard by n+m unique conductors, where n and m are any positive integers greater than one and i is any positive integer greater than one and less than or equal to nm.
 3. Apparatus in accordance with claim 2 where n and m each equal four and i equals two whereby 256 distinct characters can be defined on said keyboard by eight unique conductors.
 4. Apparatus in accordance with claim 1 wherein said responsive means comprises: a plurality of first contact members within designated switching areas on said substrate, said first contact members within each of said switching areas being connected to a respective one of said plurality of first conductors; and a plurality of second contact members within areas defined by said keys on said membrane corresponding to said switching areas, said second contact members within each of said defined areas being connected to a respective one of said plurality of second conductors, said first and second contact members being arranged for sequential connection of respective ones thereof in response to said pressure strOke.
 5. Apparatus in accordance with claim 1 wherein said one of said keys is indicative of a plurality of said characters and said responsive means is responsive to a pressure stroke applied across said one of said keys in a second direction for establishing said connections in a second one of said specified sequences and for generating said signals indicative of a second one of said characters.
 6. Appparatus for generating encoded electrical signals comprising, in combination: a keyboard structure having a plurality of keys indicative of a plurality of characters; first and second groups of conductors, a plurality of said first and second groups of conductors being associated with one of said keys; and means responsive to a pressure stroke applied across said one of said keys in a first direction for connecting said plurality of said first group of conductors to said plurality of said second group of conductors in a first sequential order and for generating signals indicative of a first one of said characters.
 7. Apparatus in accordance with claim 6 including means for grouping said signals into said first sequential order representing the keying of said first one of said characters so that errors in said keying can be reduced, comprising: first means for designating the first of said signals as the first signal in said first sequential order; first timing means for initiating a first timing period upon the completion of said first signal; second means for designating the second of said signals as the second signal in said first sequential order when said second of said signals is received before the expiration of said first timing period, said second designating means being responsive to said first timing means to reject said second of said signals and to initialize said first designating means by removing said first signal therefrom when said first timing period expires before said second of said signals is received so that signals caused by inadvertent touching of said keys can be eliminated.
 8. Apparatus in accordance with claim 7 wherein said first timing period has a duration adapted to cause rejection of signals produced by discrete pokes on said keys and to cause signals produced by strokes on said keys to be designated as signals in said first sequential order.
 9. Apparatus in accordance with claim 7 including a second timing means for initiating a second timing period when said second of said signals is received before the expiration of said first timing period; and third means for repeatedly designating said first and second of said signals as said first and second signals, respectively, in respective ones of said first sequential orders when said second of said signals has a duration greater than said second timing period, said third designating means being responsive to the termination of said second of said signals to cease operation whereby automatic repeat keying of said first one of said characters can be obtained.
 10. Apparatus in accordance with claim 7 including a third timing means responsive to the termination of said second of said signals for initiating a third timing period; and means for rejecting subsequent ones of said signals until the expiration of said third timing period thereby to eliminate signals caused by keying strokes extending beyond said one of said keys.
 11. Apparatus in accordance with claim 10 including means for reinitiating said third timing period when any signal subsequent to said second of said signals is received before the expiration of said third timing period.
 12. Apparatus in accordance with claim 6 wherein said one of said keys is indicative of a plurality of said characters and said responsive means is responsive to a pressure stroke applied across said one of said keys in a second direction for connecting said plurality of said first group of conductors to said plurality of said second group of conductors in a second sequential order and for generating sigNals indicative of a second one of said characters.
 13. Apparatus in accordance with claim 6 wherein said responsive means comprises a group of switches, a plurality of said switches being operably associated with one of said keys, a pair of said conductors from said first and second groups being associated with each of said switches for establishing a connection therebetween, said switches being arranged for operation in a first sequence in response to said pressure stroke in said first direction for connecting said conductors in said first sequential order.
 14. Apparatus in accordance with claim 13 including: means for suppressing spurious signals caused by contact bounce when said switches are operated, said suppressing means including an integration circuit; and means for controlling the duration and spacing of signals generated when said switches are operated.
 15. A keyboard each character of which is keyed by a pressure stroke in a specified direction within an area designated by said character on the surface of said keyboard to produce a preselected sequence of signals in an output circuit representing said character, comprising, in combination: a substrate having thereon a plurality of first contact members located in switching areas corresponding to said designated areas, and a plurality of first conductors each of which is connected to preselected ones of said first contact members; an insulating spacer mounted on said substrate and having apertures therein aligned with said first contact members; a resilient membrane mounted on said spacer and forming said surface of said keyboard and having said characters designated thereon, said membrane having on a major surface thereof a plurality of second contact members within said designated areas, said second contact members within a designated area being aligned with corresponding ones of said first contact members in a respective one of said switching areas through said apertures, and a plurality of second conductors each of which is connected to preselected ones of said second contact members, one of said signals being produced when one of said first conductors is connected to one of said second conductors, said membrane being adapted for movement through said apertures in response to said pressure stroke to connect said plurality of second contact members within said designated area with said corresponding ones of said first contact members within said respective switching area for connecting respective ones of said first conductors to respective ones of said second conductors, said first and second contact members being arranged for sequential connection to produce said preselected sequence of signals.
 16. A keyboard each character of which is keyed by a pressure stroke within an area defined by said character on the surface of said keyboard, said character being represented by signals generated by the connection of two first conductors with two second conductors in a specified sequence by said pressure stroke, comprising, in combination: a substrate having thereon a plurality of said first conductors and a plurality of first contact members, first and second ones of said first contact members being respectively located within first and second portions of respective switching areas designated on said substrate, first and second ones of said first conductors being respectively connected to said first and second ones of said first contact members within said first and second portions of said switching area; a spacer on said substrate having openings therethrough aligned with respective ones of said first contact members; and a deformable membrane comprising said surface of said keyboard and having said defined areas thereon, said membrane having thereon a plurality of second contact members and a plurality of said second conductors, first and second ones of said second contact members being respectively located within first and second portions of said defined area, said firSt and second ones of said second contact members in said first and second portions of said defined area being respectively aligned through said openings with said first and second ones of said first contact members in said first and second portions of a corresponding one of said switching areas, first and second ones of said second conductors being respectively connected to said first and second ones of said second contact members within said first and second portions of said defined area, said membrane being adapted for movement through said openings in response to said pressure stroke to effect contact between said first and second ones of said second contact members within said defined area and said respective first and second ones of said first contact members within said corresponding switching area in a sequential order thereby connecting said first and second ones of said first conductors, respectively, to said first and second ones of said second conductors in said specified sequence to represent said character. 